of Patients n(%) Before 1 Week 1 Month 3 Month AOD (IN PD) Surgery Post OP Post Op Post OP BIFIXATION
[less than 12(60.0%) 14(70%) 14(70%) 13(72.22%) or equal to] 60SEC MONOFIXATIO N>60SEC 8(40%) 6(30%) 6(30%) 5(27.78%) Total no of patients 20(100%) 20(100%) 20(100%) 18(100%) * * 2 patients lost follow up.
Experiment 1 confirmed that the bifixation field was significantly smaller at near convergence distances.
Bifixation refers to the images of fixated objects falling on the foveas in both eyes.
Specifically, the combination of version and vergence innervations relates to the change in size of the bifixation field as a function of viewing distance.
noted that in such extreme eye positions, it would be impossible to bifixate the target and speculated that the laws of equal innervation may only hold within the bifixation field.
Hering  also posited a mechanical and a structural factor influencing the extent of the bifixation field and the relative positions of the eyes when bifixation failed.
The first prediction is that the bifixation field is smaller for near convergence distances than for far distances, owing to increasingly incongruent vergence and version innervations at nearer viewing distances.
We measured the horizontal extent over which the eyes can move together and maintain bifixation for viewing distances of 32 cm and 125 cm.
The observers' task was to fixate the stimulus binocularly while either moving it away from their median plane (ascending trials) or moving it towards their median plane (descending trials) until it appeared misaligned (see Figure 2(b)) or aligned (see Figure 2(a)), respectively The point at which the stimulus changed from appearing misaligned (aligned) to appearing aligned (misaligned) demarked the outer horizontal limit of the bifixation field.
Within each block, the limit of the horizontal bifixation field was measured 20 times at one convergence distance (32 cm or 125 cm) and one direction of gaze (rightward or leftward).
The Relative Position of the Eyes at the Limit of the Bifixation Field.